Various types of acoustic devices have been used over the years. One example of an acoustic device is a microphone. Generally speaking, a microphone converts sound waves into an electrical signal. Microphones sometimes include multiple components that include micro-electro-mechanical systems (MEMS) components and integrated circuits (e.g., application specific integrated circuits (ASICs)).
The acoustic performance of a microphone assembly is related in part to the ratio of front volume (i.e., the volume of air between the diaphragm and the acoustic port) to back volume (i.e., the volume of the air contained by the package cavity and diaphragm) of the assembly. In typical top port devices, the components are attached directly to the substrate or base and the acoustic port is located on the top or lid, making the front volume large relative to the back volume. This is not the preferred ratio needed for optimum performance (i.e. high sensitivity, flat wideband response) of a microphone assembly.
In other configurations, the MEMS components are disposed on the lid of the assembly instead of the base. In this case, a conductive path needs to be formed so that electrical signals created by the MEMS component can reach the exterior (via conductive pads on the base). Once the electrical signals reach the exterior conductive pads, these signals can be utilized by customer circuitry, such as circuitry found in cellular phones, computers, or other devices in which the microphone resides.
MEMS microphones are typically disposed in devices such as cellular phones and personal computers. It is desirable to make these devices as small as possible. Consequently, it is desirable to make the MEMS microphones as small as possible.
Further miniaturization and cost reduction of MEMS microphones using MEMS-on-lid configurations is challenging since the wall incorporates plated through vias to establish an electrical connection between the lid and base of the microphone. The vias require considerable space on the substrate (PCB) and leave little additional room for the cavity region that is used to house the MEMS die and the integrated circuits.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.